Process to prepare adsorbents from organic fertilizer and their applications for removal of acidic gases from wet air streams

ABSTRACT

The invention is directed to an adsorbent comprising: a) 20-30% porous carbon with incorporated organic nitrogen species; and b) 70-80% inorganic matter. The invention is directed to a method of making an adsorbent which comprises: a) thermally drying dewatered sewage sludge to form granulated organic fertilizer; and b) pyrolyzing said the organic fertilizer at temperatures between 600 and 1000° C. The invention is additionally directed to the process of removing acidic gases from wet air streams comprising putting an adsorbent in contact with the wet air stream and allowing the adsorbent to adsorb the acidic gases.

[0001] This application claims the benefit of priority under 35 U.S.C.§119 based upon U.S. Ser. No. 60/253,860, filed Nov. 29, 2000, theentire disclosure of which is incorporated herein by reference.

[0002] Numerous references, including patents, patent applications andvarious publications, are cited and discussed in the description of thisinvention. The citation and/or discussion of such references is providedmerely to clarify the description of the present invention and is not anadmission that any such reference is “prior art” to the inventiondescribed herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entirety andto the same extent as if each reference was individually incorporated byreference.

1. FIELD OF THE INVENTION

[0003] The invention is directed to an adsorbent comprising: a) 20-30%porous carbon with incorporated organic nitrogen species; and b) 70-80%inorganic matter. The invention is directed to a method of making anadsorbent which comprises: a) thermally drying dewatered sewage sludgeto form granulated organic fertilizer; and b) pyrolyzing said theorganic fertilizer at temperatures between 600 and 1000° C. Theinvention is additionally directed to the processes of removing acidicgases from wet air streams comprising putting an adsorbent in contactwith the wet air stream and allowing the adsorbent to adsorb the acidicgases.

2. BACKGROUND OF THE INVENTION

[0004] Growing concerns about the environment has resulted indevelopment of new environmentally friendly technologies, new materials,and new ways to reduce and minimize wastes [Manahan, S. E. EnvironmentalChemistry, 6th ed., CRC Press: Boca Raton, Fla., 1994]. One of thewastes produced by contemporary society in abundant quantity ismunicipal sewage sludge, euphemistically often referred to as biosolids.Biosolids are a mixture of exhausted biomass generated in the aerobicand anaerobic digestion of the organic constituents of municipal sewagealong with inorganic materials such as sand and metal oxides. Accordingto the United States Environmental Protection Agency (EPA), 6.9 milliontons of biosolids (dry basis) were generated in 1998 and only 60% wereused beneficially [Biosolid Generation, Use, and Disposal in The UnitedStates: EPA530-R-99-009, September 1999; www.epa.gov]. The EPA reportestimates an annual 2% increase in the quantity of biosolids produced.

[0005] The abundance of raw sewage sludge produces one of the majorenvironmental problems of contemporary civilization. Various methodshave been proposed for its disposal [Manahan S. E. EnvironmentalChemistry, 6th ed., CRC Press: Boca Raton, Fla., 1994]. Ocean dumpingwas popular until recently, however is no longer an option because ofstricter environmental regulations [Biosolid Generation, Use, andDisposal in The United States: EPA530-R-99-009, September 1999;www.epa.gov]. Among the most often used methods of disposal arelandfilling, cropland application, and incineration [Manahan S. E.Environmental Chemistry, 6th ed.; CRC Press: Boca Raton, Fla., 1994.].Other methods that have been used to dispose of or utilize municipalsewage sludge [Biosolid Generation, Use, and Disposal in The UnitedStates: EPA530-R-99-009, September 1999; www.epa.gov], include roadsurfacing, conversion to fertilizer, compression into building blocks,and carbonization [Manahan, S. E. Environmental Chemistry, 6th ed., CRCPress: Boca Raton, Fla., 1994; Biosolid Generation, Use, and Disposal inThe United States: EPA530-R-99-009, September 1999; www.epa.gov;Sutherland, J. U.S. Pat. No. 3,998,757 (1976); Nickerson, R. D.;Messman, H. C., U.S. Pat. No.3,887,461 (1975)]. Specifically, theresidue of incineration can be used in construction materials or roadsurfacing.

[0006] Although incineration is effective in reducing the volume ofsludge and produces useful end products, cleaning of the flue gasesgenerated requires effective and expensive scrubbers. The application ofraw sewage sludge as a fertilizer produces odor problems and is alsoassociated with the risk of contamination of the soil by heavy metalsand pathogens. A more efficaceous and safer alternative is the pyrolyticcarbonization of sludge to obtain useful sorbents [Piskorz J, Scott D S,Westerberg, I B. Flash pyrolysis of sewage sludge, Ind. Proc. Des. Dev.1996; 25: 265-270; Chiang, P C., You, J H. Use of sewage sludge formanufacturing adsorbents, Can. J. Chem. Eng. 1987; 65: 922-927; Lu, G Q,Low J C F, Liu C Y, Lau A C. Surface area development of sewage sludgeduring pyrolysis, Fuel 1995; 74: 3444-3448; Lu G Q, Lau D D.Characterization of sewage sludge-derived adsorbents for H₂S removal.Part 2: surface and pore structural evolution in chemical activation.Gas Sep. Purif. 1996; 10: 103-111; Lewis F M. Method of pyrolyzingsewage sludge to produce activated carbon, U.S. Pat. No. 4,122,036(1977)].

[0007] Since 1976, several patents have been issued on carbonization ofsewage sludge and various applications of the final materials[Nickerson, R. D.; Messman, H. C., U.S. Pat. No. 3,887,461 (1975);Lewis, F. M. U.S. Pat. No. 4,122,036 (1977); Kemmer, F. N.; Robertson,R. S.; Mattix, R. D. U.S. Pat. No. 3,619,420 (1971)]. The carbonizationof sludge was first patented by Hercules, Inc. [Sutherland, J.Preparation of activated carbonaceous material from sewage sludge andsulfuric acid. U.S. Pat. No. 3,998,757(1976)]. The process was furtherinvestigated by Chiang and You [Chiang, P C., You, J H. Use of sewagesludge for manufacturing adsorbents, Can. J. Chem. Eng. 1987; 65:922-927] and Lu, et al. [Lu, G Q, Low J C F, Liu C Y, Lau A C. Surfacearea development of sewage sludge during pyrolysis, Fuel 1995; 74:3444-3448.; Lu G Q, Lau D D. Characterization of sewage sludge-derivedadsorbents for H₂S removal. Part 2: surface and pore structuralevolution in chemical activation. Gas Sep. Purif. 1996; 10: 103-111].Both simple pyrolysis and pyrolysis after addition of chemicalactivation agents such as zinc chloride or sulfuric acid were used.Carbonization of sludge in the presence of chemical activating agentssuch as zinc chloride and sulfuric acid produces new sorbents, withpatented applications in such processes as removal of organics in thefinal stages of water cleaning [Lewis, F. M. U.S. Pat. No. 4,122,036(1977)] and removal of chlorinated organics [Kemmer, F. N.; Robertson,R. S.; Mattix, R. D. U.S. Pat. No. 3,619,420 (1971)].

[0008] The process of carbonization of biosolids has been studied indetail using different chemical agents and various conditions [Chiang,P. C.; You, J. H. Can. J. Chem. Eng. 1987, 65,922; Lu, G. Q; Low J. C.F.; Liu, C. Y.; Lau A. C. Fuel 1995,74,3444; Lu, G. Q.; Lau, D. D. GasSep. Purif. 1996, 10, 103; Lu, G. Q. Environ. Tech. 1995, 16, 495]. Thesorbents obtained had relatively high surface area (100-200 m²/g forphysical activation and up to 400 m²/g for chemical activation) anddeveloped microporosity. As suggested by Chiang and You, the highcontent of inorganic matter, usually around 75%, together with themicroporosity promotes the adsorption of organic species such as methylethyl ketone or toluene [Chiang, P C., You, J H. Use of sewage sludgefor manufacturing adsorbents, Can. J. Chem. Eng. 1987; 65: 922-927]. Ingeneral, materials obtained as a result of the treatment have surfaceareas between 100 and 500 m²/g, but their performance as adsorbents hasbeen demonstrated to be much worse than that of activated carbons. Theability of these adsorbents to remove organics such as phenols, orsulfur dioxide and hydrogen sulfide [Lu, G. Q.; Lau, D. D. Gas Sep.Purif. 1996, 10, 103; Lu, G. Q. Environ. Tech. 1995, 16,495] have beentested so far; their capacity for the adsorption of SO₂ reported by Luwas less than 10% of the capacity of Ajax activated carbon [Lu, G. Q.Environ. Tech. 1995, 16, 495]. Lu and coworkers used the sorbentsobtained from sludge by chemical activation as media for the removal ofhydrogen sulfide [Lu G Q, Lau D D. Characterization of sewagesludge-derived adsorbents for H₂S removal. Part 2: surface and porestructural evolution in chemical activation. Gas Sep. Purif. 1996; 10:103-111]. Their removal capacity was only 25% of that of Calgonactivated carbons and the mechanism and efficiency of the process werenot studied in detail.

[0009] Since hydrogen sulfide is the main source of odor from sewagetreatment plants the possibility of using sewage sludge as a source ofadsorbents for H₂S is appealing. The idea is even more attractive whenthe mechanism of adsorption of hydrogen sulfide is taken into account.As proposed elsewhere [Hedden K, Huber L, Rao B R. Adsorptive Reinigungvon Schwefelwasserstoffhaltigen Abgasen V D I Bericht 1976;37: 253; AdibF, Bagreev A, Bandosz T J. Effect of surface characteristics of woodbased activated carbons on removal of hydrogen sulfide. J. Coll.Interface Sci. 1999; 214: 407-415; Adib F, Bagreev A, Bandosz T J.Effect of pH and surface chemistry on the mechanism of H₂S removal byactivated carbons. J. Coll. Interface Sci. 1999; 216: 360-369] H₂S isfirst adsorbed in the water film present on the carbon surface, followedby dissociation and adsorption of HS⁻ in the micropores. In the nextstep, HS⁻is oxidized to various sulfur species. The speciation of thefinal products of oxidation depends on the pH of the activated carbonsurface [Adib F, Bagreev A, Bandosz T J. Effect of pH and surfacechemistry on the mechanism of H₂S removal by activated carbons. J. Coll.Interface Sci. 1999; 216: 360-369; Adib F, Bagreev A, Bandosz T J.Analysis of the relationship between H₂S removal capacity and surfaceproperties of unimpregnated activated carbons. Environ. Sci. Technol.2000; 34: 686-692; Adib F, Bagreev A, Bandosz T J. Adsorption/oxidationof hydrogen sulfide on nitrogen modified activated carbons. Langmuir2000; 16: 1980-1986]. This mechanism is based on the study on unmodifiedcarbons [Adib F, Bagreev A, Bandosz T J. Effect of surfacecharacteristics of wood based activated carbons on removal of hydrogensulfide. J. Coll. Interface Sci. 1999; 214: 407-415; Adib F,Bagreev A,Bandosz T J. Effect of pH and surface chemistry on the mechanism of H₂Sremoval by activated carbons. J. Coll. Interface Sci. 1999; 216:360-369; Adib F, Bagreev A, Bandosz T J. Analysis of the relationshipbetween H₂S removal capacity and surface properties of unimpregnatedactivated carbons. Environ. Sci. Technol. 2000; 34: 686-692]. In thecase of catalytic carbons containing nitrogen it was proposed thatnitrogen-containing basic centers located in the micropores are the highenergy adsorption sites playing an important role in the oxidation ofhydrogen sulfide to sulfuric acid [Adib F, Bagreev A, Bandosz T J.Adsorption/oxidation of hydrogen sulfide on nitrogen modified activatedcarbons. Langmuir 2000; 16: 1980-1986.]. The latter as the final productmakes the regeneration feasible using simple methods such as washingwith water [Adib F, Bagreev A, Bandosz T J. On the possibility of waterregeneration of impregnated activated carbons used as hydrogen sulfideadsorbents, Ind. Eng. Chem. Res. 2000; 39: 2439-2446; Bagreev A, RahmanH, Bandosz T J. Study of H₂S adsorption and water regeneration of spentcoconut-based activated carbon. Environ. Sci. Technol. 2000; 34:4587-4592]. In the case of catalytic carbons such as Centaur® the basiccenters are introduced using the special urea modification process[Matviya T M, Hayden R A. Catalytic Carbon. U.S. Pat. No. 5,356,849(1994)]. Since sewage sludge contains a considerable amount of organicnitrogen, carbonization of such species can lead to the creation ofbasic nitrogen groups within the carbon matrix which again have beenproven to be important in the oxidation of H₂S [Adib F, Bagreev A,Bandosz T J. Adsorption/oxidation of hydrogen sulfide on nitrogenmodified activated carbons. Langmuir 2000; 16: 1980-1986; Matviya T M,Hayden R A. Catalytic Carbon. U.S. Pat. No. 5,356,849 (1994)]. Anotheradvantage to the use of sludge as a starting material is the presence ofsignificant amounts of iron added to the raw sludge as a dewateringconditioner; iron is also considered to be a catalyst for H₂S oxidation[Katoh H., Kuniyoshi I., Hirai M., Shoda M. Studies of the oxidationmechanism of sulfur containing gases on wet activated carbon fibre.Appl. Cat. B: Environ. 1995;6: 255-262; Stejns M, Mars P. Catalyticoxidation of hydrogen sulphide. Influence of pore structure and chemicalcomposition of various porous substances. Ind. Eng. Chem. Prod. Res.Dev. 1977; 16: 35-41; Cariaso, O. C. and Walker P L. Oxidation ofhydrogen sulphide over microporous carbons. Carbon 1975; 13: 233-239].

[0010] Primarily caustic-impregnated carbons have been used asadsorbents of hydrogen sulfide at sewage treatment plants. Because ofthe presence of KOH or NaOH their pH is high, which ensures thathydrogen sulfide is oxidized to elemental sulfur. The process is fastand caustic impregnated carbons have high hydrogen sulfide breakthroughcapacity. Such materials have a H₂S breakthrough capacity measured usingaccelerated test (not suitable for virgin carbons and other adsorbents),which should be around 140 mg/g. In one example of its use, the New YorkCity Department of Environmental Protection installed 118 carbon vesselsin 12 sewage treatment plants. Each vessel contains about 10 tons ofactivated carbon adsorbent.

[0011] Caustic-impregnated carbons, although efficient for H₂S removal,have many disadvantages which recently have attracted the attention ofresearchers toward alternative sorbents, unmodified activated carbons.The disadvantages of caustic-impregnated carbons are as follows:

[0012] 1) Limited capacity for physical adsorption of VOCs (volatileorganic compounds) due to the presence of caustic materials in thecarbon pore system.

[0013] 2) Low self-ignition temperature, which may result in fire insidethe carbon vessel.

[0014] 3) Special safety precautions in dealing with caustic materialshave to be applied.

[0015] 4) High density because of the presence of water.

[0016] 5) Higher cost than that of unmodified carbons.

[0017] The results of recent studies have shown that at very lowconcentrations of hydrogen sulfide (as is present at sewage treatmentplants), unmodified carbons can work effectively as adsorption/oxidationmedia. Thus, there is a great interest in the development of new typesof adsorbents for use in sewage treatment facilities.

3. SUMMARY OF THE INVENTION

[0018] This invention is directed to an adsorbent comprising: a) 20-30%porous carbon with incorporated organic nitrogen species; and b) 70-80%inorganic matter. This invention is further directed to a method ofmaking an adsorbent which comprises thermally drying dewatered sewagesludge to form granulated organic fertilizer and pyrolyzing said theorganic fertilizer at temperatures between 600 and 1000° C. Thisinvention is directed to the process of removing acidic gases from wetair streams comprising putting an adsorbent comprising 20-30% porouscarbon with incorporated organic nitrogen species and 70-80% inorganicmatter in contact with the wet air stream and allowing the adsorbent toadsorb the acidic gases. This invention is further directed to theprocess of removing acidic gases from wet air streams comprising formingan adsorbent by thermally drying dewatered sewage sludge to formgranulated organic fertilizer and pyrolyzing said organic fertilizer attemperatures between 600-1000° C., putting said adsorbent in contactwith the wet air stream, and allowing the adsorbent to adsorb the acidicgases.

4. BRIEF DESCRIPTION OF THE FIGURES

[0019]FIG. 1. (A) TG, (B) DTG, and (C) DTA curves for pyrolysis ofsludge-derived fertilizer in air (solid heavy lines) and nitrogen (solidthin lines).

[0020]FIG. 2. Nitrogen adsorption isotherms for ash and the sludgederived materials.

[0021]FIG. 3. Development of porosity with increasing pyrolysistemperature.

[0022]FIG. 4. Pore size distributions for ash and the sludge derivedmaterials.

[0023]FIG. 5. Comparison of the pore size distribution for SLC-1 andSLC-3 and their acid-washed counterparts.

[0024]FIG. 6. pKa distributions for the materials studied.

[0025]FIG. 7. FTIR curves for the initial sludge, ash and SLC-2 andSLC-4.

[0026]FIG. 8. FTIR curves for SLC-1 and SLC-3 and their acid-washedcounterparts.

[0027]FIG. 9. H₂S breakthrough curves for initial sludge-derivedadsorbents and sludge-derived adsorbents after acid treatment.

[0028]FIG. 10. Comparison of the H₂S breakthrough curves obtained forSC-4, SC-4A and S208 and S208-Fe.

[0029]FIG. 11. Changes in pore size distributions for the sludge-derivedsamples before and after H₂S adsorption.

[0030]FIG. 12. Changes in pore size distributions for S208 series ofsamples before and after H₂S adsorption.

[0031]FIG. 13. Specific H₂S adsorption vs temperature of heat treatment.

[0032]FIG. 14. DTG curves in nitrogen for the sludge-derived adsorbentsand their acid-treated counterparts.

[0033]FIG. 15. DTG curves in nitrogen for the S208 series of samples.

[0034]FIG. 16. Changes in capacity with an increase in residence time(bed depth) for sludge-derived sorbent (950° C.) and coconut-shell-basedactivated carbon (S208 from Bamabey and Sutcliffe). The capacitymeasured for caustic-impregnated carbon is marked as open boxes.

[0035]FIG. 17. H₂S breakthrough curves for our sorbents and commercialcarbons (12 mL bed).

5. DETAILED DESCRIPTION OF THE INVENTION

[0036] Some of the terms of the invention may be defined as follows.

[0037] Adsorption: The surface of a solid always accumulates moleculesfrom its gaseous or liquid environment; this phenomenon is calledadsorption.

[0038] Adsorbent: A material that is able to adsorb considerable amountsof gases or vapors under certain conditions.

[0039] Pyrolysis: Heat treatment (over 400° C.) in an inert atmosphereof materials having organic origin.

[0040] Activated carbon: A carbonaceous material obtained by pyrolysisof organic precursors (coal, wood, peat, etc.) at elevated temperaturesfollowed by their activation using various physical or chemical agents(at temperatures between 600 and 1000° C.).

[0041] Caustic-impregnated carbon: Activated carbons impregnated withKOH or NaOH in order to increase their pH and adsorption capacity foracidic gases.

[0042] Breakthrough capacity: The amount of substance adsorbed on thesorbent surface until the substance is detected in effluent air at acertain concentration level.

[0043] Acidic gases: Gases able to be transformed into acids or gasesable to interact as acids (electron acceptors).

[0044] Specific surface area: The surface area per unit weight ofadsorbent considered to be the area where adsorption of variousmolecules can occur.

[0045] Pore volume: The volume of pores in adsorbent calculated asavailable to nitrogen molecules at its boiling point.

[0046] Oxidation: Change in the chemical stage of a substance associatedwith an electron loss. The charge on the species becomes more positive.

[0047] Residence time: An average time to be spent by reactant moleculesin order to pass through the reactor.

[0048] This invention is directed to an adsorbent comprising: a) 20-30%porous carbon with incorporated organic nitrogen species; and b) 70-80%inorganic matter. In one embodiment, the inorganic matter includeshighly dispersed catalytic oxides. In a further embodiment, thecatalytic oxides are one or more of copper oxide, zinc oxide, ironoxide, calcium oxide, silica and alumina. In another embodiment, thenitrogen species comprises amine or pyridine groups. In one embodiment,the surface area of the adsorbent is 100-500 m²/g. In a furtherembodiment, the surface area of the adsorbent is 100-200 m²/g. Inanother embodiment, the adsorbent contains micropores and the volume ofthe micropores are at least 0.03 cm³/g. In one embodiment, the pH of theadsorbent is greater than 10. In another embodiment, the pH of theadsorbent is between 7 and 10. In another embodiment, the pH of theadsorbent is between 4 and 7.

[0049] The adsorbents of this invention have several advantages:

[0050] 1) Sorbents obtained from sewage sludge-derived organicfertilizer have two-fold higher capacity for hydrogen sulfide removalthan unmodified carbons.

[0051] 2) Their capacity is comparable to that of caustic-impregnatedcarbons used worldwide as hydrogen sulfide adsorbents in sewagetreatment plants.

[0052] 3) The kinetics of the removal process are very fast and no heatis released.

[0053] 4) During adsorption H₂S reacts with inorganic matter and isoxidized to elemental sulfur. The product is environmentally inert. ThepH of the spent material is about 7 so it can be safely discarded.

[0054] 5) Since the sorbents are obtained from sewage sludge thesignificant amount of municipal waste can be recycled and reused insewage treatment plants.

[0055] 6) The sorbents can be also used in desulfurization of gaseousfuel and in hydrothermal vents.

[0056] 7) The sorbents can find another environmental application inremoval of SO₂ in effluent gas from power plants.

[0057] 8) The possibility exists of regeneration of spent materialsusing heating to 300° C. to remove elemental sulfur and sulfur dioxide.

[0058] This invention is further directed to a method of making anadsorbent which comprises: a) thermally drying dewatered sewage sludgeto form granulated organic fertilizer; and b) pyrolyzing said theorganic fertilizer at temperatures between 600 and 1000° C. In oneembodiment, the heating rate is between 5 and 10° C./minute and the holdtime is between 60 and 90 minutes. In a further embodiment, thetemperature of pyrolysis is between 800 and 1000° C. In a furtherembodiment, the temperature of pyrolysis is between 900 and 1000° C. Ina further embodiment, the temperature of pyrolysis is between 600 and900° C. and the adsorbent is further treated with 15-20% HCl. In afurther embodiment, the temperature of pyrolysis is between 800 and 900°C. The invention is additionally directed to an adsorbent formed by oneof the above-identified methods.

[0059] The invention is directed to the process of removing acidic gasesfrom wet air streams comprising putting an adsorbent comprising 20-30%porous carbon with incorporated organic nitrogen species and 70-80%inorganic matter in contact with the wet air stream and allowing theadsorbent to adsorb the acidic gases. In one embodiment, the acidicgases are one or more of hydrogen sulfide, sulfur dioxide, hydrogencyanide, and nitrogen dioxide. In another embodiment, the acidic gas ishydrogen sulfide which reacts with inorganic matter to be oxidized tosulfur dioxide or elemental sulfur and salt forms thereof. In a furtherembodiment, the wet air stream is effluent from a sewage treatmentplant, gaseous fuel, or gases from hydrothermal vents.

[0060] The invention is directed to the process of removing acidic gasesfrom wet air streams comprising forming an adsorbent by thermally dryingdewatered sewage sludge to form granulated organic fertilizer andpyrolyzing said organic fertilizer at temperatures between 600-1000° C.,putting said adsorbent in contact with the wet air stream, and allowingthe adsorbent to adsorb the acidic gases. In one embodiment, the acidicgases are one or more of hydrogen sulfide, sulfur dioxide, hydrogencyanide, and nitrogen dioxide. In another embodiment, the temperature ofpyrolysis is between 800 and 1000° C. In a further embodiment, thetemperature of pyrolysis is between 900 and 1000° C. In anotherembodiment, the temperature of pyrolysis is between 600 and 900° C. andthe adsorbent is further treated with 15-20% HCl. In another embodiment,the temperature of pyrolysis is between 800 and 900° C. In anotherembodiment, the adsorbent may be regenerated by heating to 300-500° C.to remove elemental sulfur and sulfur dioxide.

6. EXAMPLES

[0061] A. Materials (SLC-1, SLC-2, SLC-3, SLC-4, C-1, and C-3)

[0062] Terrene® was obtained from NYOFCo (New York Organic FertilizerCompany) in the form of 3 mm diameter granules with about 5% watercontent. (Terrene® is a registered trademark of Wheelabrator Clean WaterSystems, Inc., Hampton, N.H.) The results of the chemical analysis (PaceAnalytical Services) are presented in Table 1. The adsorbents studiedwere prepared by pyrolysis of Terrene® at temperatures between 400-950°C. in a nitrogen atmosphere in a fixed bed (horizontal furnace). Thesamples, experimental pyrolysis conditions, and adsorbent yieldcalculated as the weight ratio after and before pyrolysis are given inTable 2. To determine the effect of acid washing on the pore structureand chemistry of the organic carbonaceous phase, the SLC-1 and SLC-3samples were subsequently treated with 16% hydrochloric acid to removeacid-soluble inorganic matter and then washed with distilled water toremove excess acid. The samples obtained in this way are designated asC-1 and C-3, respectively. TABLE 1 Results of chemical analysis ofTerrene ® Content Element/quantity [ppm] Aluminum 7410 Arsenic 5.97Cadmium 3.52 Calcium 20300 Chromium 73.2 Cobalt 10.2 Copper 932 Iron26600 Lead 280 Magnesium 5550 Molybdenum 13.2 Nickel 44.6 Potassium 0.09Selenium 6.09 Silver ND Zinc 1290 Sulfur 0.70% Nitrogen 1.82% Phosphorus3.17% pH 7.08 Bulk density 0.78 g/cm³ Density 1.21 g/cm³ Fixed solids65.3% Volatile solids 34.7%

[0063] TABLE 2 Names of samples, conditions of preparation and yields ofcarbonaceous materials Yield of Temper- Heating Hold Yield of Ashcarbon. Sample ature rate time adsorbents content material name [° C.][deg/min] [min] [%] [%] [%] SLC-1 400 10 30 51.9 61.7 19.9 SLC-2 600 1060 46.3 69.1 14.3 SLC-3 800 10 60 41.8 76.8 9.7 SLC-4 950 10 60 39.380.7 7.6 Ash 600 5 120 33.1 — —

[0064] B. Materials (SC-1, SC-2, SC-3, SC-4, SC-2A, SC-3A, SC-4A, S208,S208-Fe and Derivatives)

[0065] Terrene® was obtained from the New York Organic FertilizerCompany, (Bronx, N.Y.) in the form of 3 mm diameter granules with about5% water content. It contains around 35% inorganic matter mainly in theform of iron, alumina, silica oxides and carbonates. The adsorbentsstudied were prepared by pyrolysis of Terrene® at temperatures between400-950° C. in a nitrogen atmosphere in a fixed bed (horizontalfurnace). The samples are referred to as SC-1, SC-2, SC-3 and SC-4 where1, 2, 3, and 4 represent the pyrolysis temperatures of 400, 600, 800 and950° C., respectively. To determine the effect of metals such as iron,zinc and copper, the samples were treated with 18% hydrochloric acid forthree days followed by washing with distilled water to remove excessHCl. The samples obtained in this way are designated as SC-2A, andSC-3A, and SC-4A. The filtrates were saved to determine the quantitiesof removed metals as described below.

[0066] For comparison, the experiments were done using the as-receivedcarbon manufactured from coconut shells by Watelink Bamabey andSutcliffe, S208. The sorbent is produced in the form of 6.4×3.2 mmpellets. To provide the same dynamic conditions of the experiment, S208carbon was granulated and the fraction with the same size (1-3 mm) asthe carbonized Terrene® was chosen for the breakthrough experiments.

[0067] To study the effect of iron, a 20 g subsample of the S208 carbonwas impregnated with 40 ml ferric chloride (5%). The sample was thenhydrolyzed in the presence of dilute sodium hydroxide, filtered, anddried. The material was then heated under the same conditions as SC-4(950° C.). The sample is referred to as S208-Fe.

[0068] The breakthrough tests were also carried out on activated alumina(Alcoa®, S_(BET)=309 m²/g, V_(t)=0.37 cm³/g) as received and with ironoxides introduced in the same way as described above for S208—Fe. Thesamples are referred to as Al₂O₃ and Al₂O₃—Fe.

[0069] The prepared materials were studied as hydrogen sulfideadsorbents in the dynamic tests described below. After exhaustion of itsadsorbent capacity, each sample is identified by adding the letter “E”to its designation.

[0070] C. Methods of Making Organic Fertilizer

[0071] The adsorbents of this invention may be made from any thermallydried dewatered biosolid, organic fertilizer, as a precursor. In oneembodiment, Terrene® obtained from NYOFCo (New York Organic FertilizerCompany) in the form of 3 mm diameter granules with about 5% watercontent, may be used as the precursor to the adsorbent. Thermally drieddewatered biosolids may be made by the following general method(Wheelabrator Technologies, Inc.). Dewatered biosolids cake is mixedwith recycled dry biosolids to produce a granular feed for dryers, suchas rotary dryers. The resulting biosolids are dried to approximatelyfive percent water content in the dryers. If a rotary dryer is used, thetumbling action of the dryers creates round pellets, which may beseparated by size. Pellets of the desired size may be separated andundersized and crushed pellets may be recycled for use as recycled driedbiosolids in the first step of producing granular feed for the dryers.

[0072] D. Methods of Studying Materials

[0073] Nitrogen Adsorption

[0074] Nitrogen adsorption isotherms were measured using an ASAP 2010analyzer (Micromeritics, Norcross, Ga., USA) at −196° C. Before theexperiment, the samples were degassed at 120° C. to constant pressure of10⁻⁵ torr. The isotherms were used to calculate the specific surfacearea, S_(N2) or S_(DFT); micropore volume, V_(mic); total pore volume,V_(t); and pore size distribution. All the parameters were determinedusing Density Functional Theory (DFT) [Lastoskie C M, Gubbins K E,Quirke N. Pore size distribution analysis of microporous carbons: adensity functional theory approach. J. Phys. Chem. 1993; 97: 4786-4796;Olivier J P. Modeling physical adsorption on porous and nonporous solidsusing density functional theory. J. Porous Materials 1995; 2: 9-17] andthe Dubinin-Raduskevich (DR) method [Dubinin M M. In Chemistry andPhysics of Carbon; Walker, P. L., Ed.; Vol.2. Marcel Dekker: New York,1966; Jagiello J, Bandosz T J, Schwarz J A. Carbon surfacecharacterization in terms of its acidity constant distribution Carbon1994; 32: 1026-1028]. The relative microporositywas calculated as theratio of micropore volume (DR) to total pore volume. In some cases, BETsurface area, S_(BET), and the total pore volume, V_(t) (evaluated fromthe last point of the isotherm) were calculated.

[0075] Potentiometric Titration

[0076] Potentiometric titration measurements were performed with a DMSTitrino 716 automatic titrator (Metrohm, Brinkmann Instruments,Westbury, N.Y., USA). The instrument was set in the mode when theequilibrium pH was collected . Approximately 0.100 g samples were placedin a container thermostated at 298 K with 50 mL of 0.01M NaNO₃ andequilibrated overnight. To eliminate interference by CO₂, the suspensionwas continuously saturated with N₂. The carbon suspension was stirredthroughout the measurement. The titrant was standardized 0.1 M NaOH.Experiments were carried out in the pH range 3-10 and the results weretreated using a method used in the art [Jagiello J, Bandosz T J, PutyeraK, Schwarz J A. Determination of proton affinity distributions forchemical systems in aqueous environments using stable numerical solutionof the adsorption integral . J. Coll. Interface Sci 1995; 172: 341-346;Bandosz T J, Buczek B, Grzybek T, Jagiello, J. Determination of surfacechanges in active carbons by potentiometric titration and wateradsorption Fuel 1997; 76:1409-1417].

[0077] DRIFT

[0078] Diffuse reflectance IR spectra were obtained using a NicoletImpact 410 FT-IR spectrometer equipped with a diffuse reflectance unit(Nicolet Instrument Corp., Madison, Wis., USA). Adsorbent carbon powderswere placed in a micro-sample holder.

[0079] pH

[0080] A 0.4 g sample of dry adsorbent was added to 20 mL of water andthe suspension stirred overnight to reach equilibrium. The sample wasfiltered and the pH of solution was measured using a Accumet Basic pHmeter (Fisher Scientific, Springfield, N.J., USA).

[0081] Thermal Analysis

[0082] Thermal analysis was carried out using TA Instruments ThermalAnalyzer (New Castle, Del., USA). The heating rate was 10° C./min inanitrogen atmosphere at 100 mL/min flow rate. TGA is thermogravimetricanalysis. DTA is differential thermal analysis. DTG is differentialthermogravimetric analysis. TG is thermogravimetry.

[0083] CHN Analysis

[0084] Carbon, nitrogen and hydrogen analyses were performed by HuffmanLaboratories, Golden, Colo., USA.

[0085] H₂S Breakthrough Capacity

[0086] The dynamic tests were carried out at room temperature toevaluate the capacity of sorbents for H₂S removal. Adsorbent sampleswere packed into a column (length 60 mm, diameter 9 mm, bed volume 6cm³) and prehumidified with moist air (relative humidity 80% at 25° C.)for an hour. The amount of adsorbed water was estimated from theincrease in the sample weight. Moist air (relative humidity 80% at 25°C.) containing 0.3% (3000 ppm) H₂S was then passed through the column ofadsorbent at 0.5 L/min. The elution of H₂S was monitored using anInterscan LD-17 H₂S continuous monitor system interfaced with a computerdata acquisition program. The test was stopped at the breakthroughconcentration of 500 ppm. The adsorption capacities of each sorbent interms of g of H₂S per gram of carbon were calculated by integration ofthe area above the breakthrough curves, and from the H₂S concentrationin the inlet gas, flow rate, breakthrough time, and mass of sorbent.

[0087] Determination of Iron, Zinc and Copper

[0088] The quantities of iron, zinc and copper removed fromsludge-derived adsorbents during acid treatment were determined using aComputrace 716 polarograph (Netrohm) in the differential pulse mode.0.03 M triethanolamine was the electrolyte used for the determination ofiron, whereas copper and zinc were determined using a 0.05 M NH₃/NH₄Clbuffer solution. In all cases, the standard addition method was appliedwith 1 niL sample and 10 mL supporting electrolyte. The differentialpulse polarography peaks for iron, zinc and copper were at −1.04, −1.07,and −0.30 V vs. SCE, respectively.

[0089] E. Results and Discussion Concerning Materials SLC-1, SLC-2,SLC-3, SLC-4, C-1, and C-3

[0090] The analytical data in Table 1 shows the thermally-dried sludgepellets (Terrene®) have a high content of inorganic matter, especiallymetals such as iron and calcium, which can be beneficial in thecatalytic oxidation of hydrogen sulfide [Katoh H., Kuniyoshi I., HiraiM., Shoda M. Studies of the oxidation mechanism of sulfur containinggases on wet activated carbon fibre. Appl. Cat. B: Environ. 1995;6:255-262.]. As expected for this digested municipal sludge product, theorganic nitrogen, phosphorus and sulfur content is also high. Theanalysis does not include carbon, but based on the results of previousstudies, the total organic matter in the sludge product is expected tobe about 70% (w/w) [Chiang, P C., You, J H. Use of sewage sludge formanufacturing adsorbents, Can. J. Chem. Eng. 1987; 65: 922-927; Lu, G Q,Low J C F, Liu C Y, Lau A C. Surface area development of sewage sludgeduring pyrolysis, Fuel 1995; 74: 3444-3448; Lu G Q, Lau D D.Characterization of sewage sludge-derived adsorbents for H₂S removal.Part 2: surface and pore structural evolution in chemical activation.Gas Sep. Purif. 1996; 10: 103-111]. The ash content of the sample wasevaluated using thermal analysis. The residue after heating the sludgepellets to 1000° C. is 31.4% of the initial sample mass, which is inagreement with previous studies [Chiang, P C., You, J H. Use of sewagesludge for manufacturing adsorbents, Can. J. Chem. Eng. 1987; 65:922-927; Lu, G Q, Low J C F, Liu C Y, Lau A C. Surface area developmentof sewage sludge during pyrolysis, Fuel 1995; 74: 3444-3448; Lu G Q, LauD D. Characterization of sewage sludge-derived adsorbents for H₂Sremoval. Part 2: surface and pore structural evolution in chemicalactivation. Gas Sep. Purif. 1996; 10: 103-111]. About 80% of the ash isexpected to consist of inorganic oxides such as Al₂O₃, SiO₂, Fe₂O₃ [Lu,G Q, Low J C F, Liu C Y, Lau A C. Surface area development of sewagesludge during pyrolysis, Fuel 1995; 74: 3444-3448].

[0091] The results of the thermal analysis of the sludge pellets in airand in nitrogen are presented in FIG. 1. The TGA curves in air andnitrogen are similar up to about 275° C. (FIGS. 1A and 1B). The firstpeak at about 125° C. is the result of the removal of water (around 4%).The weight loss observed between about 200° C. and 400° C. is the resultof the emission of volatile organic compounds responsible for the strongunpleasant odor during carbonization. In air, the sharp decrease inweight at 275° C. correlates with the first, smaller DTA exotherm (FIG.1C), caused by oxidation and/or volatilization of easily oxidizedvolatiles in the sludge pellets. The corresponding weight change in thenitrogen atmosphere maximizing at about 340° C. reflects volatilizationof these compounds. A second, similar event is observed at about 425° C.More significant differences occur at temperatures greater than 450° C.In the air atmosphere, ignition of the carbonaceous material occurs asindicated by the sharp exotherm on the DTA and weight derivative curveon the TGA scan. The DTA curve in nitrogen (FIG. 1C) is almostfeatureless.

[0092] The weight losses clearly seen on the DTG curves in FIG. 1B arequantified in Table 3. The total yield of adsorbent is 39.1% with 80.3%content of ash. The yield of carbonaceous phase is up to 19.7%. TABLE 3Weight loss during thermal analysis of Terrene ® [%] Atmosphere 30-200°C. 200-500° C. 500-1000° C. Total yield nitrogen 7.2 42.8 10.9 60.9 39.1air 7.4 48.1 13.1 68.6 31.4

[0093] The results of the thermal analysis of Terrene® were used tochoose the experimental conditions for the pyrolysis, and as shown inTable 2, 400, 600, 800 and 950° C. were chosen as pyrolysistemperatures. As expected, the yield of carbonaceous phase calculatedfrom thermal analysis decreases with an increasing temperature of heattreatment, and ranges from 19.5% for SLC-1 to 7.6% for SLC-4.

[0094] The results of CHN analysis in Table 4, show that the sorbentsobtained have about 30% carbonaceous material which is good for thedevelopment of the surface features responsible for physical adsorption.Also as expected, the sample SLC-1 has the highest content of nitrogen,almost 4%. With increasing carbonization temperature both the nitrogenand hydrogen contents decrease because of both loss of volatile speciesand increase in the degree of carbonization. Moreover, the organicnitrogen that is probably present as proteinaceous amine functionalitiesin the low temperature carbonized material is gradually transformed intopyridine-like compounds (see below) which should be reflected inincreased basicity of the surface. After washing with hydrochloric acid% of carbon and nitrogen increase because of the partial removal ofinorganic matter. It is worth noting that the nitrogen content of theC-3 sample increased 18% compared to its unwashed precursor, which maybe beneficial for the application of this material as a sorbent foracidic gases. The dissolution of inorganic matter by acid treatment ofSLC-1 and SLC-3 resulted in weight losses of 26% and 19%, respectively.TABLE 4 Carbon, hydrogen, and nitrogen content [%] (elemental analysis).Sample C H N SLC-1 28.19 2.04 3.83 SLC-2 27.14 1.14 3.19 SLC-3 26.370.42 1.61 SLC-4 24.89 0.35 0.94 C-1 36.92 2.46 4.79 C-3 31.97 0.63 1.90

[0095] The pore structure of adsorbents was determined using sorption ofnitrogen at its boiling point. The adsorption isotherms are presented inFIG. 2. It is clearly seen that the total sorption uptake increases withincreasing pyrolysis temperature. The isotherms are characteristic ofpredominantly mesoporous solids with some contribution by themicropores. The surface areas and pore volumes calculated using the DRand DFT methods are given in Table 5. The surface area increases by afactor of almost three as the pyrolysis temperature is increased from400 to 950° C. The biggest difference exists between SLC-1 and SLC-2suggesting that significant development of the porosity occurs between400 and 600° C. Similar changes are observed for micropore volumes,which reach 0.051 cm³/g for SLC-4 (DR method). The relativemicroporosity, defined as the ratio of the volume of micropores to totalpore volume, is almost constant for the samples heated to temperatureshigher than 600° C. Its values near 30% indicate a significantcontribution of mesoporosity in the sludge-derived adsorbents. Themesopores may have their origin in the high (˜80%) content of inorganicmatter, which consists mainly of silica, alumina, and iron oxides[Jagiello J, Bandosz T J, Putyera K, Schwarz J A. Determination ofproton affinity distributions for chemical systems in aqueousenvironments using stable numerical solution of the adsorption integral.J. Coll. Interface Sci 1995; 172: 341-346]. To determine thecontribution of the mesopores, the adsorption isotherms were measured onthe ash obtained after heating the sample in air at 600° C. (FIG. 2).The ash surface area is quite small which reflects the presence mainlyof mesopores (Table 5). The development of porosity with increasingpyrolysis temperature is demonstrated in FIG. 3. TABLE 5 Structuralparameters calculated from nitrogen adsorption isotherms. S_(BET)V_(mic)(DR) S_(mic)(DR) S_(DFT) V_(mic)(DFT) V_(t)(0.99*) Sample [m²/g][cm³/g] [m²/g] [m²/g] [cm³/g] [cm³/g] V_(mic)/V_(t) SLC-1 41 0.016 35 210.006 0.084 0.19 SLC-2 99 0.044 108 92 0.030 0.131 0.33 SLC-3 104 0.048118 106 0.033 0.132 0.36 SLC-4 122 0.051 120 104 0.028 0.158 0.32 C-1 170.006 13 15 0.002 0.063 0.09 C-3 139 0.058 135 150 0.030 0.201 0.29 Ash20 0.008 17 13 0.003 0.077 0.10

[0096] The pore size distributions (PSDs) calculated for our materialsusing density functional theory [Lastoskie C M, Gubbins K E, Quirke N.Pore size distribution analysis of microporous carbons: a densityfunctional theory approach. J. Phys. Chem. 1993; 97: 4786-4796; OlivierJ P. Modeling physical adsorption on porous and nonporous solids usingdensity functional theory. J. Porous Materials 1995; 2: 9-17] are shownin FIGS. 4 and 5. The development of micropores (smaller than 20 Å) isobserved with increasing carbonization temperature. Moreover, the volumeof mesopores smaller than 100 Å significantly increases with temperatureas a result of chemical changes in the inorganic matter andcarbon-inorganic matter interface. These PSDs also confirm ourhypothesis about the source of the mesoporosity being the inorganicmatter. FIG. 5 shows the changes in the distribution of pore sizes forsamples before and after acid washing. For the sample carbonized at 400°C., a significant decrease in the volume of pores of all sizes isobserved on acid washing, a result of the chemical reactivity of thissample. After pyrolysis at low temperature both organic and inorganicstructures have a high reactivity toward acids resulting in asignificant change in the physical state of the material. On the otherhand, for the sludge pellet sample treated at 800° C., acid washingproduces a significant increase in the volume of micro- and smallmesopores along with a decrease in the volume of mesopores. It is likelythat acid washing removes species such as iron oxides, creating newpores within the inorganic matter and at the interface between theinorganic and organic phases. An increase in the total porosity is alsoa result of the increasing contribution of the carbonaceous material inthis sample.

[0097] All the structural parameters reported in Table 5 are muchsmaller than those for commercial activated carbons [Bansal R C, DonnetJ B, Stoeckli F. Active Carbon; Marcel Dekker: New York, 1988].Considering that our sorbents contain 25 to 30% carbon, the porousstructure responsible for an increase in the surface area has to bedeveloped within this organic deposit. Since a higher pore volume isgenerated simultaneously with lower carbon content, the increase inpyrolysis temperature must produce subtle chemical changes resulting ingasification of carbon and creation of more pore volume. The small peaksin the DTG curves at 700° C. and 800° C. may reflect these changes. Thechemical changes may be related to an increase in the degree ofaromatization and the incorporation of nitrogen and other heteroatomsinto the carbon matrix [Adib F, Bagreev A, Bandosz T J.Adsorption/oxidation of hydrogen sulfide on nitrogen modified activatedcarbons. Langinuir 2000; 16: 1980-1986.; Stohr B, Boehm H P. Enhancementof the catalytic activity of activated carbons in oxidation reactions bythermal treatment with ammonia of hydrogen cyanide and observation of asuperoxide species as a possible intermediate. Carbon 1991; 29, 707-720;Schmiers H, Friebel J, Streubel P, Hesse R, Kopsel R. Change of chemicalbonding of nitrogen of polymeric n-heterocyclic compounds duringpyrolysis. Carbon 1999; 37: 1965-1978]. Moreover, water released fromdehydroxylation of inorganic material can act as a pore former andactivation agent creating very small (Angstrom-size) pores in the carbondeposit [Bandosz T J, Putyera K, Jagiello J, Schwarz J A. Study ofcarbon smectite composites and carbons obtained by in situ carbonizationof polyfurfuryl alcohol. Carbon 1994; 32, 659-664; Bandosz T J, JagielloJ, Putyera K, Schwarz J A. Sieving properties of carbons obtained bytemplate carbonization of polyfurfuryl alcohol within mineral matrices.Langmuir 1995; 11: 3964-3969; Bandosz T J, Jagiello J, Putyera K,Schwarz J A. Pore structure of carbon-mineral nanocomposites and derivedcarbons obtained by template carbonization. Chem. Mat. 1996; 8:2023-2029].

[0098] The suggested chemical changes described above reflected first inthe pH values of the adsorbents (Table 6). It is interesting that the pHof the sample SLC-1 is close to neutral and that pyrolysis at highertemperatures causes a significant increase in the pH values to greaterthan pH 11. The pH of the ash sample is also close to neutral. Since thedehydroxylation of inorganic species is expected to occur at around 400°C. [Barrer R M. Zeolites and Clay Minerals as Sorbents and MolecularSieves: Academic Press; London 1978] an increase of 3.8 pH units betweenSLC-1 and SLC-2 must be related to chemical changes in the carbon phase.These samples have high organic nitrogen contents. When the pyrolysistemperature is higher than 600° C. this nitrogen is probablyincorporated into the carbon matrix as heteroatoms such as pyridine-likestructures [Adib F, Bagreev A, Bandosz T J. Adsorption/oxidation ofhydrogen sulfide on nitrogen modified activated carbons. Langmuir2000;16: 1980-1986.; Stohr B, Boehm H P. Enhancement of the catalyticactivity of activated carbons in oxidation reactions by thermaltreatment with ammonia of hydrogen cyanide and observation of asuperoxide species as a possible intermediate. Carbon 1991; 29, 707-720;Schmiers H, Friebel J, Streubel P, Hesse R, Kopsel R. Change of chemicalbonding of nitrogen of polymeric n-heterocyclic compounds duringpyrolysis. Carbon 1999; 37: 1965-1978]. The basicity of these centerscontributes to the high pH of the sludge-derived adsorbents. TABLE 6 pHvalues of adsorbents' surface. Sample pH SLC-1  7.72 SLC-2 11.51 SLC-311.29 SLC-4 10.96 Ash  8.27

[0099] Changes in the surface chemistry were further studied usingpotentiometric titrations. The procedure applied and the mathematicaltreatment of the data [Jagiello J, Bandosz T J, Schwarz J A. Carbonsurface characterization in terms of its acidity constant distributionCarbon 1994; 32: 1026-1028; Jagiello J, Bandosz T J, Putyera K, SchwarzJ A. Determination of proton affinity distributions for chemical systemsin aqueous environments using stable numerical solution of theadsorption integral. J. Coll. Interface Sci 1995; 172: 341-346; BandoszT J, Buczek B, Grzybek T, Jagiello, J. Determination of surface changesin active carbons bypotentiometric titration and water adsorption Fuel1997; 76:1409-1417; Bandosz T J, Jagiello J, Schwarz J A., Surfaceacidity of pillared taeniolites in terms of their proton affinitydistributions J. Phys.Chem. 1995; 99, 13522-13527] yields thedistributions of acidity constants. The results are presented in FIG. 6.Comparisons of the peak intensities and peak positions indicate thepredominant effect of the inorganic matrix on the acidity of thesamples. The peaks for the high temperature sludge-derived samples aresimilar to those present in ash. Heat treatment results in changes inthe acidity due to dehydroxylation of inorganic matter and rearrangementin coordination of such metals as alumina or iron [Bandosz T J, JagielloJ, Schwarz J A., Surface acidity of pillared taeniolites in terms oftheir proton affinity distributions J. Phys.Chem. 1995; 99, 13522-13527;Bandosz T J, Cheng K. Changes in acidity of Fe pillared/delaminatedsmectites on heat treatment J. Colloid Interface Sci., 1997; 191:456-463; Lu, G Q, Low J C F, Liu C Y, Lau A C. Surface area developmentof sewage sludge during pyrolysis, Fuel 1995; 74: 3444-3448]. It isinteresting that the sample carbonized at 600° C., SLC-2, differssignificantly in acidity from the other samples. This is not consistentwith the pH values in Table 6. The reason for the discrepancy may lie ina limitation of the potentiometric titration method, which is able todetect species having pKa's between 3 and 11. Species present with pKa'sbeyond the experimental window will affect the average pH of the sample.In the case of SLC-2 is likely the significant in inorganic/organicphase occur at the temperature, which also results in a significantincrease in the porosity evaluated from nitrogen adsorption

[0100] Comparison of the pKa distributions for SLC-1 and SLC-3 revealsdifferences in the peak intensities of peak at pKa's of approximately3.5, 8.6, and 5.5. At the higher carbonization temperature the number ofspecies having pKa's near 5.5 significantly decreased relative to thespecies with pKa's near 3.5 or 8.6. The observed effect is related tothe changes in the acidity of inorganic oxides. After acid washing thedistributions become more consistent with each other except for the peakat pKa near 7. In the case of C-1 this peak almost disappears whereas inC-3 the amount of detected species is much lower than for SLC-3. Thepeak probably represents soluble iron oxides [Bandosz T J, Cheng K.Changes in acidity of Fe pillared/delaminated smectites on heattreatment J. Colloid Interface Sci., 1997; 191: 456-463]. In C-1 thesedecreased about 97% vs. a decrease of about 62% for C-3, relative to thenon-acid washed material.

[0101] The surface chemistry of the sewage sludge-derived samples wasalso studied using DRIFT. The results are presented in FIGS. 7 and 8. Inthe spectra obtained for the sludge-derived samples carbonized at thelowest temperature, the well-defined features of the inorganic matterare seen. For higher carbonization temperatures the spectra become moresimilar to those characteristic of activated carbons, reflecting thecombined effects of the “screening” action of carbon, dehydroxylation ofthe mineral matter and possible phase transitions.Washing with acidchanges the chemistry which is reflected in changes in the relativeintensities of peaks. The distinctive feature of the low temperaturecarbonized samples, SLC-1 and C-1 is the presence of a peak between 2750and 3000 cm⁻¹ which likely represents the nitrogen in aminefunctionalities. If as suggested above amine nitrogen is converted intopyridine form at high temperatures, peaks around 1575 cm⁻¹ should beapparent [The Sandtler Handbook of Infrared Spectral. Simons W W, Ed.,Sandtler Research Laboratories, Inc. 1978]. Although in the spectra forour samples this peak is present we can not rule out other species suchas —COO— bonds [Bandosz T J, Lin C, Ritter J A. Porosity and surfaceacidity of SiO₂—Al₂O₃ J.Coll. Interface Sci. 1998; 198: 347-353 ] whichabsorb in this region.

[0102] Significant changes in the chemical and physical nature ofcarbon-mineral sorbents are obtained by pyrolysis of a thermally-driedsewage sludge fertilizer product, Terrene®. Sorbents having surfaceareas up to 140 m²/g can be derived using a simple carbonization method.The materials have broad pore distributions with about 30% of total porevolume in very small micropores. The unique surface chemistry resultsfrom a combination of acidity from metal oxides such as silica, alumina,or iron, and basicity from organic nitrogen in the form of amine orpyridine-like groups. The presence of basic nitrogen and iron can holdsignificant advantages for the application of these materials assorbents for acidic gases.

[0103] F. Results and Discussion Concerning Materials SC-1, SC-2, SC-3,SC-4, SC-2A, SC-3A, SC-4A, S208, S208-Fe and Derivatives

[0104] The H₂S breakthrough curves for our samples before and after acidtreatment are shown in FIGS. 9A and 9B. For comparison, FIG. 10 showsthe curves obtained for coconut shell-based activated carbon, asreceived and after impregnation with iron. The calculated capacities aresummarized in Table 7. It is clearly seen that with increasing pyrolysistemperature the capacity of the sludge-derived adsorbents issignificantly increased. It is remarkable that the capacity of thesample treated at 950° C., SC-4, is twice that of the as receivedactivated carbon. After acid treatment, the breakthrough time of SC-4Adecreased around 30% whereas for SC-2A and SC-3A an increase was found.The breakthrough curve for the latter sample resembles the curveobtained for SC-4A. Indeed their calculated capacities are comparable.In spite of the observed decrease in the performance of the acid treatedsample carbonized at 950° C., removal of inorganic oxides generallyincreased the capacities of the samples carbonized at low temperature.It also changed the surface acidity. The initial materials are mainlybasic. After acid washing their pH decreased to about 3, which may berelated to the removal of basic oxides and to the strong adsorption ofhydrochloric acid in the small pores. The ability of samples to retainwater is also altered. After acid treatment twice as much water wasadsorbed on the surface. As indicated elsewhere [Hedden, K.; Huber. L.;Rao, B. R. V D I Bericht 1976, 37, 253], the presence of water onactivated carbons enhances the dissociation of hydrogen sulfide andfacilitates to its oxidation to sulfur and sulfur dioxide [Adib, F.;Bagreev, A.; Bandosz, T. J. Environ. Sci. Technol. 2000,34, 686; Hedden,K.; Huber. L.; Rao, B. R. V D I Bericht 1976, 37, 253; Adib, F.;Bagreev, A.; Bandosz, T. J. J. Coll. Interface Sci. 1999, 214, 407;Adib, F.; Bagreev, A.; Bandosz, T. J J. Coll. Interface Sci. 1999, 216,360]. In the case of the sludge-derived materials, the mechanism ofhydrogen sulfide removal probably differs from that for activatedcarbons. For the activated carbons, the significant decrease in theadsorption capacity corresponding to exhaustion is usually caused by theformation of sulfuric acid [Adib, F.; Bagreev, A.; Bandosz, T. J.Environ. Sci. Technol. 2000, 34, 686; Adib, F.; Bagreev, A.; Bandosz, T.J J. Coll. Interface Sci. 1999, 216, 360]. For the sludge-derivedsamples, only a small decrease in pH is observed and after exhaustionthe materials preserve their basic pH. As was pointed out elsewhere[Adib, F.; Bagreev, A.; Bandosz, T. J. Environ. Sci. Technol. 2000, 34,686; Adib, F.; Bagreev, A.; Bandosz, T. J. J. Coll. Interface Sci.1999,214,407; Adib, F.; Bagreev, A.; Bandosz, T. J J. Coll. InterfaceSci. 1999, 216, 360], for conventional carbons, basic initial pH favorsthe formation of elemental and polymeric sulfur as the final products ofoxidation; there is a threshold pH below which this process becomesinfeasible. However, this rule probably does not apply to oursludge-derived materials. For acid treated samples, even at very low pH,the capacity is still significant. Also noteworthy is the decrease in pHafter exhaustion, which suggests formation of sulfuric acid [Adib, F.;Bagreev, A.; Bandosz, T. J. Environ. Sci. Technol. 2000, 34, 686; Adib,F.; Bagreev, A.; Bandosz, T. J J. Coll. Interface Sci. 1999, 216, 360;Adib, F.; Bagreev, A.; Bandosz, T. J. Langmuir 2000, 16, 1980]. Thesedifferences indicate that the mechanisms of hydrogen sulfide removal oninitial and acid treated samples differ from each other. The differencesare probably caused by the catalytic effect of inorganic matter [Katoh,H.; Kuniyoshi, I.; Hirai, M.; Shoda, M. Appl. Cat. B: Environ. 1995, 6,255; Stejns, M.; Mars, P. Ind. Eng. Chem. Prod. Res. Dev. 1977, 16, 35;Cariaso, O. C.;Walker, P. L. Carbon 1975, 13, 233]. The possibility ofchemisorption in the process of H₂S removal on sludge-derived carbon wasalso pointed out by Lu and Lou; however, the capacity of their adsorbentwas reported to be only 25% of that of activated carbon chosen for acomparison [Lu, G. Q.; Lau, D. D. Gas Sep. Purif. 1996,10,103]. Aremarkably good performance of the SC-4 carbon as a hydrogen sulfideadsorbent also indicates that differences in the mechanisms of theprocess exist within the series of materials, probably attributable tochanges in their chemical and structural composition. TABLE 7 pH of thematerials studied, their H₂S breakthrough capacities, and the quantityof water adsorbed during prehumidification. H₂S breakthrough capacityWater adsorbed Sample pH (mg/g) (mg/g) SC-1 7.9  8.2 60 SC-1E 7.5 — —SC-2 11.4  14.9 40 SC-2E 9.2 — — SC-3 11.2  23.6 48 SC-3E 8.8 — — SC-410.8  82.6 62 SC-4E 9.9 — — SC-2A 2.8 21.2 106  SC-2AE 2.5 — — SC-3A 4.062.3 94 SC-3AE 2.3 — — SC-4A 3.8 57.5 100  SC-4AE 2.7 — — S208 10   48.877 S208E 7.4 — — S208-Fe 7.4 104.5  165  S208-FeE 2.0 — — Al₂O₃ 8    0  30 Al₂O₃—E — — Al₂O₃—Fe 8   6.5 23 Al₂O₃— — — FeE

[0105] Since the sludge-derived materials are rich in catalytic metalssuch as iron, zinc, copper, and aluminum oxides (Chiang, P. C.; You, J.H. Can. J. Chem. Eng. 1987, 65, 922) the differences in the performanceof adsorbents before and after acid treatment are probably related tothe presence of these metals in various forms, depending on thetemperature treatment. Table 8 shows that the weight of the samplesdecreased between 20 to 30% after acid treatment. This is related to theremoval of a significant amount of inorganic oxides. Even though acidtreatment was done under the same conditions for all samples, the sampleheated at 950° C. seems to be the most acid resistant. It is possiblethat heating at 950° C. resulted in the formation of mineral-likecompounds with very high dispersion of catalytically active metaloxides. The effects of acid treatment on the content of iron, zinc andcopper are summarized in Table 8. Metal contents in the initialmaterials were calculated based on ICP analyses. The data indicate thatalmost all iron was removed after treatment, while zinc and copper wereremoved only partially. It is interesting that the efficiency of theprocess decreased with increasing heat treatment temperature whichsupports our hypothesis about the formation of mineral-like structuresin the case of sample SC-4. Only a very small percentage of copper andzinc were removed from this sample. Nevertheless, even after removal ofall iron the capacities of SC-2A and SC-3A increased. This maybe relatedto the changes in the dispersion of catalytically active metals (otherthan iron) resulting from reactions of oxides with acid, and an increasein the sample porosity [Adib, F.; Bagreev, A.; Bandosz, T. J. Langmuir2000, 16, 1980; Stejns, M.; Mars, P. Ind. Eng. Chem. Prod. Res. Dev.1977, 16, 35]. TABLE 8 Weight loss as a result of acid treatment,content of iron, zinc, and copper in the sludge derived materials(mg/g). Sample Weight loss(%) Fe Zn Cu SC-2 58 2.79 2.01 SC-2A 27  01.75 0.52 SC-3 64 3.09 2.22 SC-3A 25  0 2.23 1.79 SC-4 68 3.28 2.37SC-4A 19  5 3.15 2.89

[0106] Since the capacity of SC-4A decreased after acid treatment andremoval of iron, the effect of this metal on the adsorption/oxidation ofhydrogen sulfide on activated alumina and coconut shell-based carbonwere studied. The results are given in Table 7. For both adsorbents,after impregnation with iron oxide the capacity for H₂Sadsorption/oxidation increased significantly. In the absence of iron,activated alumina was not able to immobilize any hydrogen sulfide. Afterimpregnation and exposure to H₂S for a short time, the surface changedcolor from orange-brown to black suggesting the presence of ironsulfide. Interesting results were obtained for the ironoxide-impregnated coconut shell-based carbon. The capacity increasedsignificantly to a level slightly higher than the capacity of thesludge-derived adsorbent, SC-4. This increase in the H₂S removalcapacity upon impregnation of carbons with metal oxides capable ofcreating stable sulfides is not unexpected. Impregnation is well knownin the activated carbon industry as a method to increase the performanceof materials [Radovic, L. R.; Sudhakar, Ch. In Introduction to CarbonTechnologies, Marsh, H; Heintz, E. A.; Rodriguez-Reinoso, F. (Eds.)University of Alicante, Alicante, Spain,1997, p103]. It is worthpointing out here that after this treatment the performance of thecoconut shell-based carbon is only slightly better than that of SC-4,and that the breakthrough curves (FIG. 10) are very similar.Nevertheless, the differences between the two materials must lie in theproducts of oxidation. While the surface pH of exhausted SC-4E decreasedonly slightly, that of S208-FeE became very acidic suggesting asignificant quantity of sulfuric acid adsorbed on the carbon surface[Adib, F.; Bagreev, A.; Bandosz, T. J. Environ. Sci. Technol. 2000, 34,686; Adib, F.; Bagreev, A.; Bandosz, T. J. Langmuir 2000, 16, 1980].

[0107] The demonstration of the superiority of the performance of thesludge-derived adsorbents would not be complete without the detailedanalysis of the pore structure and its comparison to coconut shell basedactivated carbon. Structural parameters calculated from nitrogenadsorption isotherms are given in Table 9. The surface area and porevolumes increase with increasing carbonization temperature. It isnoteworthy that there are no significant differences in the porosity ofSC-3 and SC-4 which could explain the differences in their H₂Sadsorption capacity. This supports our hypothesis that significantchanges in surface chemistry favorable to H₂S chemisorption occur whenthe sludge is pyrolyzed at 950° C. TABLE 9 Structural parameterscalculated from nitrogen adsorption isotherms and estimated hypotheticalsulfur volume (assuming density equal to 2 g/cm³). S_(BET) S_(DFT)V_(mic) V_(t)(0.995*) ΔV_(mic) ΔV_(t) V_(sulf) Sample (m²/g) (m²/g)(cm³/g) (cm³/g) V_(mic)/V_(t) (cm³/g) (cm³/g) (cm³/g) SC-1 41 21 0.0060.075 0.080 SC-1E 12 8 0.003 0.057 0.053 0.003 0.018 0.004 SC-2 99 920.030 0.115 0.261 SC-2E 14 9 0.001 0.040 0.025 0.029 0.075 0.007 SC-3104 106 0.033 0.107 0.308 SC-3E 14 9 0.003 0.064 0.047 0.030 0.043 0.013SC-4 122 104 0.028 0.100 0.280 SC-4E 21 13 0.002 0.065 0.031 0.026 0.0350.039 SC-2A 186 181 0.039 0.107 0.364 SC-2AE 15 12 0.002 0.011 0.1810.037 0.096 0.010 SC-3A 193 196 0.040 0.113 0.354 SC-3AE 8 8 0.001 0.0110.090 0.039 0.102 0.029 SC-4A 181 183 0.042 0.119 0.352 SC-4AE 86 950.018 0.085 0.212 0.024 0.034 0.027 S208 880 889 0.359 0.457 0.786 S208E781 774 0.352 0.414 0.850 0.070 0.043 0.023 S208-Fe 933 932 0.406 0.4980.815 S208- 560 528 0.243 0.294 0.827 0.163 0.204 0.049 FeE

[0108] After H₂S adsorption/oxidation, the surface areas and porevolumes significantly decreased. This decrease is especially apparent inthe volume of micropores indicating that they are active in theadsorption/oxidation process. Assuming that sulfur is the oxidationproduct deposited in these pores, the volume of deposited sulfur(density assumed to be 2 g/cm³) can be calculated based on the amount ofhydrogen sulfide adsorbed. The values are presented in Table 9 asV_(sulf). For samples obtained at 800° C. and lower temperatures thevolume of sulfur is much smaller than the decrease in the pore volumesuggesting either the blockage of the pore entrances or the presence ofother sulfur compounds such as sulfides on the surface. On the otherhand, for the SC-4E sample the decrease in the micropore volume (and thetotal pore volume) is less than the calculated volume of sulfur. Thisindicates not only that all the pores of this material are completelyfilled with sulfur but that sulfur must be also chemisorbed on thesurface in the form of chemical compounds.

[0109] As shown in Table 9, after acid treatment the surface area andpore volumes increased almost 100%. This may contribute to the observedincrease in the H₂S breakthrough capacity of SC-2 and SC-3. Changes inthe structural parameters upon exhaustion follow the trend observed forthe initial samples. The only apparent difference is in the behavior ofthe SC-4AE sample, which lost only 50% of the surface area and microporevolume (compared to SC-4A) and which has a calculated sulfur volumesmaller than the total decrease in the pore volume. In fact the value ofV_(sulf) is almost equal to a decrease in the volume of micropores,ΔV_(mic), which suggests deposition of sulfur in pores smaller than 20Å. This apparent change in the mechanism of sulfur immobilization isprobably caused by the removal of iron and other catalytically activemetals, which prevents chemisorption and the formation of new compounds.Differences in the relative microporosity expressed as the ratio of thevolume of micropores to the total pore volume further supportdifferences in the immobilization mechanism between SC-3A and SC-4A.Although for both samples the quantities of adsorbed hydrogen sulfideare similar the relative microporosity decreased only 40% for the lattersample vs.about 75% for the SC-3A. Once again this suggests that sulfurspecies deposit at the pore entrances of SC-3A blocking theiraccessibility for the adsorption process.

[0110] Differences in the mechanism of the hydrogen sulfideimmobilization before and after impregnation with iron are seen from ananalysis of the structural parameters obtained for the coconutshell-based samples (Table 9). It is interesting that the surface areaand pore volumes slightly increased after impregnation with iron oxide,suggesting a contribution of the iron deposit to porosity development.After H₂S adsorption on the initial sample, the volume of microporesdecreased only 0.007 cm³/g, much less than the calculated volume ofsulfur deposited on this carbon (0.023 cm³/g). This finding indicatesthat in this case sulfur is adsorbed in the mesopores. After treatmentwith iron a significant decrease in the volume of micropores is found.Since this decrease is almost three times larger than the calculatedvolume of sulfur, the deposited species must block the entrances to themicropores as was observed for some sludge-derived samples.

[0111] Detailed changes in microporosity caused by hydrogen sulfideadsorption/oxidation are seen from the analysis of the pore sizedistributions (PSD) presented in FIG. 11. PSD's were calculated usingdensity functional theory [Lastoskie, C. M.; Gubbins, K. E.; Quirke, N.J. Phys. Chem. 1993, 97, 4786; Olivier, J. P. J. Porous Materials 1995,2, 9]. For the initial samples, development of small pores is observedwith increasing heat treatment temperature. All the sludge-derivedsamples have a significant development of mesoporosity as a result ofthe presence of inorganic matter. It is probable that microporosityexists in the carbonaceous deposit (around 30% of total mass of theadsorbent) or/and on the interface between carbon and inorganic matter.It is clearly seen that after H₂S adsorption almost all the microporesdisappear; the volume of mesopores decreased but not as drastically asthe volume of micropores. A similar result is found for the acid-treatedsamples. As a result of the removal of inorganic matter (around 25% byweight) the contribution of the carbonaceous material to the total massof the adsorbent increased, increasing the volume of the micropores.Mesopores, however present, are not so dominant as in the case of theinitial materials. After adsorption, nearly all the pores disappear forall samples except SC-4A. This indicates that the pore entrances areblocked by the adsorption/oxidation products. In the case of SC-4E, itis mainly the pores smaller than 50 Å that are affected. Although thevolume of small pores is still available to nitrogen molecules, it isnot active in the process of hydrogen sulfide adsorption. This isprobably the result of the fouling effect of sulfur or/and sulfuric acidon the catalytic properties of the adsorbents [Stejns, M.; Mars, P. Ind.Eng. Chem. Prod. Res. Dev. 1977, 16, 35; Coskun, I.; Tollefson, E. L.Can. J. Chem. Eng. 1986, 58, 72; Ghosh, T. K.; Tollefson, E. L. Can. J.Chem. Eng. 1986, 64, 960].

[0112] Similar trends were observed for activated carbons in which evenafter exhaustion a significant volume of micropores was still availablefor nitrogen adsorption [Adib, F.; Bagreev, A.; Bandosz, T. J. Environ.Sci. Technol. 2000, 34, 686; Adib, F.; Bagreev, A.; Bandosz, T. J. J.Coll. Interface Sci. 1999, 214, 407; Adib, F.; Bagreev, A.; Bandosz, T.J J. Coll. Interface Sci. 1999, 216, 360; Adib, F.; Bagreev, A.;Bandosz, T. J. Langrnuir 2000, 16, 1980]. Indeed, this is noticed forthe S208 carbon before and after impregnation with iron (FIG. 12). Ifthe “catalytic efficiency” of this carbon for hydrogen sulfideimmobilization was similar to that of SC-4, its capacity would be muchhigher because of the larger pore volume. Unfortunately, this is not thecase even after impregnation with iron.

[0113] Differences in the performance of the materials studied arevisualized in the bar diagram (FIG. 13), which presents the specificcapacity (capacity divided by surface area, in mg/m²) versus the thermaltreatment temperature. The diagram clearly shows that for allsludge-derived carbons except SC-4, the performances of each aresimilar, suggesting that the mechanism of immobilization is similar. Theperformance of the acid treated samples except SC-4 is also similar. Theexception of the SC-4 sample supports the hypothesis that catalyticcenters are formed at 950° C. For comparison, the specific capacities ofthe S208 and S208-Fe samples are 0.05 mg/m² and 0.19 mg/m²,respectively. These low values clearly demonstrate the superiority ofthe surface features of the sludge-derived SC-4 adsorbent crucial forhydrogen sulfide adsorption/oxidation.

[0114] As discussed elsewhere [Adib, F.; Bagreev, A.; Bandosz, T. J.Environ. Sci. Technol. 2000, 34, 686; Adib, F.; Bagreev, A.; Bandosz, T.J. J. Coll. Interface Sci. 1999, 214, 407; Adib, F.; Bagreev, A.;Bandosz, T. J J. Coll. Interface Sci. 1999, 216, 360], when activatedcarbons are used as hydrogen sulfide adsorbents, H₂S is oxidized toeither sulfur or sulfuric acid. The presence of sulfuric acid isdemonstrated by the low temperature peak in the DTG curves (between200-300° C.), and the presence of sulfur by the peak centered at about400° C. [Adib, F.; Bagreev, A.; Bandosz, T. J. Environ. Sci. Technol.2000, 34, 686; Adib, F.; Bagreev, A.; Bandosz, T. J. J. Coll. InterfaceSci. 1999, 214, 407; Rodriguez-Mirasol, J.; Cordero, T.; Rodriguez, J.J. Extended Abstracts of 23rd Biennial Conference on Carbon, CollegePark, July 1997 p. 376; Chang, C. H. Carbon 1981, 19, 175]. Usually agood correlation is found between the amount of hydrogen sulfideadsorbed on an activated carbon and the amount of species determinedusing thermal analysis. However, applying the same approach to thesludge-derived materials revealed a significant discrepancy between theamount of sulfur adsorbed and that detected using the TA method. Theresults are summarized in Table 10 and FIG. 14. Although for some of oursamples the two peaks representing sulfur and sulfur dioxide arepresent, the amount of sulfur as these species was only 20% to 50% ofthe total sulfur adsorbed. The SO₂ peak is well defined (with a shoulderrepresenting sulfur) only for the SC-4E sample. This suggests thatheating to 950° C. caused the changes in surface chemistry and porositythat enhanced the selectivity for oxidation of H₂S to SO₂ (Table 10).Changes in this direction also occur after acid treatment, especiallyfor the SC-3A sample where a relatively narrow peak centered at 250° C.is found on the DTG curve. Although in the case of the SC-4A sample theintensity of this peak did not change compared to SC-4, the peakrepresenting elemental sulfur is much more pronounced after acidwashing. This finding suggests that the presence of iron and othermetals (removed during acid washing) favor SO₂ as the reaction product.This is reflected in the changes in the pH of the samples afterexhaustion (Table 7). The decrease is more pronounced for acid treatedsamples than for their initial counterparts. It is necessary to mentionhere that the discussion above is limited only to two common products ofH₂S oxidation, SO₂ and elemental sulfur. TABLE 10 Weight loss (%) at thetemperature ranges related to the presence of the products of H₂Soxidation and estimated amount of sulfur from break- through capacitytest (S _(B.Th)) and thermal analysis (S_(TA)) Selectivity for SO₂150-350 350-500 500-700 oxidation Sample ° C. ° C. ° C. S_(TA) S _(B.Th)(%) SC-1 3.38 — — — — — SC-1E 2.57 — — N/A 0.77 — SC-2 1.73 1.83 — 20.2SC-2E 2.19 1.61 — 0.23 1.14 — SC-3 0.47 0.23 0.82 13.1 SC-3E 1.05 0.560.49 0.62 2.22 — SC-4 0.12 0.01 0.07 16.1 SC-4E 2.62 1.05 0.08 3.73 7.76— SC-2A 2.42 2.64 — 15.8 SC-2AE 3.05 2.98 — 0.66 1.99 — SC-3A 1.17 0.931.19 35.2 SC-3AE 5.30 1.65 1.30 2.79 5.86 — SC-4A 1.44 0.52 0.08 20.3SC-4AE 3.64 1.07 0.78 1.65 5.41 — S208 1.01 0.79 — 15.4 S208E 2.42 1.94— 1.86 4.58 — S208-Fe 0.34 0.17 — 36.9 S208-FeE 7.57 2.78 — 6.23 9.81 —

[0115] Failure to account for all the sulfur deposited on the surfacesuggests that new species are formed whose decomposition temperaturesare higher than the 1000° C. used in our experiment. Even if we assumethat FeS_(x) is a reaction product in the form of troilite (FeS, meltingpoint: 1193-1200° C.) or pyrite (FeS₂, melting point: 1171° C.) its DTGpeak should appear at temperatures as high as 1200° C. [Handbook ofChemistry and Physics, 67th ed.,Weast, R. C. Ed. CRC press, BocaRaton,Fla., 1986]. Indeed, when the SC-4E sample was heated to 1300° C. theintensity of a peak centered between 1000° C. and 1200° C. almostdoubled (FIG. 14). Although this temperature is higher than the sludgecarbonization temperature, such a significant increase in intensityindicates the formation of new species as a result of exposure tohydrogen sulfide. If other catalytically active metals are present theirsulfur compounds are expected to be even more thermally stable. Sincethe presence of SO₂ in the effluent gas was checked experimentally andeliminated as a possibility, the only conclusion we can draw at thisstage of our study is that sulfur chemically bonds to metal oxidespresent in the mineral-like forms.

[0116] The presence of iron also affects the selectivity of oxidation ofH₂S on the S208 carbon. After iron impregnation, more sulfuric acid isformed (FIG. 15) as demonstrated by the significant decrease in pH(Table 7) and the increase in the intensity in the DTG peak at about230° C. Also supporting the significant role of iron in the selectivityof H₂S oxidation for the S208-FeE sample is the only slight increase inthe intensity of the peak assigned to sulfur. As a result of surfacemodification more H₂S was adsorbed and all of it was converted to sulfurdioxide.

[0117] Based on the data presented above, the sludge-derived adsorbent,SC-4, has superior capacity for hydrogen sulfide adsorption. It performsmuch better than the coconut shell-based microporous carbon adsorbentscurrently under consideration as alternatives to caustic-impregnatedcarbons in sewage treatment plants. On the surface of the sludge-derivedadsorbent, hydrogen sulfide is immobilized mainly in the form of sulfurand other compounds resulting from interactions of H₂S with mineral-likemetal oxides containing iron, zinc, copper, and/or others. Under ourexperimental conditions, the capacity of the best sludge-derivedadsorbents is exhausted when all pores are filled with the oxidationproducts.

[0118] G. Results and Discussion Concerning Materials Pyrolyzed atTemperatures Between 800-1000° C.

[0119] Organic fertilizer, Terrene®, was pyrolyzed in anitrogenatmosphere at 800-1000° C. for 1 hour with heating rate 10 deg/min. As aresult, a new adsorbent was obtained. It consists porous activatedcarbon (around 20%) with incorporated organic nitrogen species andinorganic matter (around 80%) with highly dispersed catalytic oxidessuch as iron, copper, zinc and calcium oxides, alumina, silica, etc. Thespecific surface areas and micropore volumes calculated using DFT(Density Functional Theory) method are around 120 m²/g and 0.050 cm³/g,respectively.

[0120] The adsorbents obtained are used to remove hydrogen sulfide andother acidic gases (such as sulfur dioxide) from wet air streams. Theperformance test was designed in our lab and the conditions aredescribed in the literature [Adib, Bagreev and Bandosz, J. ColloidInterface. Sci. 214, 407-415, 1999]. The results showed that thebreakthrough capacity of the new adsorbent is comparable to the capacityfor caustic-impregnated activated carbons and greater than that forcoconut-based carbon (FIG. 17). The latter material is an alternativesorbent recently under consideration to replace caustic-impregnatedactivated carbon commonly used to remove hydrogen sulfide from effluentair in sewage treatment plants. Table 11 shows the capacity of thesample pyrolyzed at 950° C. The capacity increases with an increasingbed size (increasing residence time), however, at residence time around1.3 second (similar to the residence time at sewage treatment plant) thereaction is close to completion and the capacity become more or lessconstant. The trend is shown in FIG. 16. In FIG. 16 we also report theperformance of the coconut-shell based carbon measured under the sameconditions. The capacity measured for caustic-impregnated carbon is alsonoted. TABLE 11 Changes in the performance of the adsorbent pyrolyzed at950° C. with increasing size of the bed. Residence Breakthrough- H₂SAds. Weight Volume Depth time Time At 500 ppm at 500 ppm [g] [cm³] [cm][sec] [min] [mg/g] 1.2 3 4 0.2 50 53 3.9 6 8 0.3 157 81 4.0 6 8 0.3 12665 7.7 6 16 0.6 770 202 15.1 12 31 1.2 1885 259 26.9 24 54 2.0 3770 291

[0121] The analysis of the performance of samples pyrolyzed at varioustemperatures indicates that significant chemical changes in the natureof adsorbent occur between 800 and 950° C. resulting in a four-foldincrease in the capacity (FIG. 13). The surface area and microporevolume increase only 20% for the sample pyrolyzed at 950° C. compared tothat pyrolyzed at 800° C.

[0122] On the surface of the new adsorbent, hydrogen sulfide ischemically bonded to metal compounds creating stable sulfides andsulfide-like species. Moreover, the surface, due to the presence ofcatalytic metals and basic nitrogen groups catalyzes oxidation ofhydrogen sulfide to elemental sulfur. The process continues until thepore structure is completely filled with oxidation products. The pH ofthe spent material is close to neutral. Table 12 shows the changes inthe surface area, S, and pore volumes (total pore volume, Vt, and volumeof micropores, V_(mic)) for the samples (pyrolyzed at 800 and 950° C.)before and after H₂S adsorption. TABLE 12 Changes in the surface area,S_(N2), and pore volumes (total pore volume, V_(t), and volume ofmicropores, V_(mic)) for the samples (pyrolyzed at 800 and 950° C.)before and after H₂S adsorption. (Bed volume - 6 mL) S_(N2) afterV_(mic)-after V_(t)- after S _(N2)-initial H₂S ads. V_(mic)-initial H₂Sads. V_(t)- initial H₂S ads Sample [m²/g] [m²/g] [cm³/g] [cm³/g] [cm³/g][cm³/g] 800° C. 104 17 0.044 0.008 0.132 0.066 950° C. 122 21 0.0510.009 0.158 0.081

What is claimed is:
 1. An adsorbent comprising: a) 20-30% porous carbonwith incorporated organic nitrogen species; and b) 70-80% inorganicmatter.
 2. The adsorbent of claim 1, wherein the inorganic matterincludes highly dispersed catalytic oxides.
 3. The adsorbent of claim 2,wherein the catalytic oxides are one or more of copper oxide, zincoxide, iron oxide, calcium oxide, silica and alumina.
 4. The adsorbentof claim 1, wherein the nitrogen species comprises amine or pyridinegroups.
 5. The adsorbent of claim 1, wherein the surface area of theadsorbent is 100-500 m²/g.
 6. The adsorbent of claim 5, wherein thesurface area of the adsorbent is 100-200 m²/g.
 7. The adsorbent of claim1, wherein the adsorbent contains micropores and the volume of themicropores are at least 0.03 cm³/g.
 8. The adsorbent of claim 1, whereinthe pH of the adsorbent is greater than
 10. 9. The adsorbent of claim 1,wherein the pH of the adsorbent is between 7 and
 10. 10. The adsorbentof claim 1, wherein the pH of the adsorbent is between 4 and
 7. 11. Amethod of making an adsorbent which comprises: a) thermally dryingdewatered sewage sludge to form granulated organic fertilizer; and b)pyrolyzing said the organic fertilizer at temperatures between 600 and1000° C.
 12. The method of claim 11, wherein the heating rate is between5 and 10° C./minute and the hold time is between 60 and 90 minutes. 13.The method of claim 11, wherein the temperature of pyrolysis is between800 and 1000° C.
 14. The method of claim 13, wherein the temperature ofpyrolysis is between 900 and 1000° C.
 15. The method of claim 11,wherein the temperature of pyrolysis is between 600 and 900° C. and theadsorbent is further treated with 15-20% HCl.
 16. The method of claim15, wherein the temperature of pyrolysis is between 800 and 900° C. 17.An adsorbent formed by the method of claim
 11. 18. The process ofremoving acidic gases from wet air streams comprising putting anadsorbent comprising 20-30% porous carbon with incorporated organicnitrogen species and 70-80% inorganic matter in contact with the wet airstream and allowing the adsorbent to adsorb the acidic gases.
 19. Theprocess of claim 18, wherein the acidic gases are one or more ofhydrogen sulfide, sulfur dioxide, hydrogen cyanide, and nitrogendioxide.
 20. The process of claim 18, wherein the acidic gas is hydrogensulfide which reacts with inorganic matter to be oxidized to sulfurdioxide or elemental sulfur and salt forms thereof.
 21. The process ofclaim 18, wherein the wet air stream is effluent from a sewage treatmentplant, gaseous fuel, or gases from hydrothermal vents.
 22. The processof removing acidic gases from wet air streams comprising forming anadsorbent by thermally drying dewatered sewage sludge to form granulatedorganic fertilizer and pyrolyzing said organic fertilizer attemperatures between 600-1000° C., putting said adsorbent in contactwith the wet air stream, and allowing the adsorbent to adsorb the acidicgases.
 23. The process of claim 22, wherein the acidic gases are one ormore of hydrogen sulfide, sulfur dioxide, hydrogen cyanide, and nitrogendioxide.
 24. The process of claim 22, wherein the temperature ofpyrolysis is between 800 and 1000° C.
 25. The process of claim 24,wherein the temperature of pyrolysis is between 900 and 1000° C.
 26. Theprocess of claim 22, wherein the temperature of pyrolysis is between 600and 900° C. and the adsorbent is further treated with 15-20% HCl. 27.The process of claim 26, wherein the temperature of pyrolysis is between800 and 900° C.
 28. The process of claim 22, wherein the adsorbent maybe regenerated by heating to 300-500° C. to remove elemental sulfur andsulfur dioxide.